JP2017533451A - Dielectric polarization beam splitter - Google Patents

Abstract

The present invention is a dielectric polarizing beam splitter (10, 20a, 20b, 30, 40) comprising a grating layer (13) disposed on a substantial plane of a substrate (11). The grating layer may include an elongated, substantially parallel, alternating array of high index regions (13H) and low index regions (13L). The refractive index (nL) of the low refractive index region can be lower than the refractive index (nH) of the high refractive index region.

Description

  The present application relates generally to optical devices called polarizing beam splitters, or reflective wire grid polarizers.

  Many optical systems require the use of polarized light. A polarizing beam splitter can split light into two lights having opposite polarization states. Each type of polarizing beam splitter has drawbacks. The MacNeil prism has the disadvantage that the range of light incident angles is small. Wire grid polarizing beam splitter plates allow a much wider range of light incidence angles compared to MacNeille prisms, but with relatively low efficiency, long back focal length in optics and fragile properties As a result, it may have a drawback that it is difficult to assemble into an optical system. Some wire grid polarizing beam splitters in the cube can overcome back focal length and wire grid polarizing beam splitter plate assembly problems, but are less efficient compared to wire grid polarizing beam splitter plates There is. The materials used for polarizers usually absorb large amounts of light. In some applications, it is important to minimize any loss of light due to absorption.

  Wide range of light incident angle, high transmittance of one polarization (for example, high Tp), high reflection of opposite polarization is controlled (for example, Rs is high or Rs is controlled to a desired value) Providing a polarizing beam splitter that is highly efficient, has a short back focal length of the optical system, is easy to assemble into the optical system, and has minimal loss of light due to absorption. It is believed that it can be advantageous. The present invention relates to various embodiments of a dielectric polarizing beam splitter (PBS) for the visible spectrum that meets these needs. Each embodiment may meet one, some, or all of these needs. The PBS may comprise a lattice layer disposed in a substantial plane of the substrate. The grating layer includes an array of alternating high and low refractive index regions that are elongated and substantially parallel.

1 is one of schematic cross-sectional side views of a dielectric polarizing beam splitter, according to an embodiment of the present invention. FIG. 1 is one of schematic cross-sectional side views of a dielectric polarizing beam splitter, according to an embodiment of the present invention. FIG. 1 is one of schematic cross-sectional side views of a dielectric polarizing beam splitter, according to an embodiment of the present invention. FIG. 1 is one of schematic cross-sectional side views of a dielectric polarizing beam splitter, according to an embodiment of the present invention. FIG. 1 is a schematic perspective view of a dielectric polarizing beam splitter, according to an embodiment of the present invention, showing non-vertical incident light L _xz at an angle θ _{xz in} the _xz plane. FIG. 1 is a schematic perspective view of a dielectric polarizing beam splitter according to an embodiment of the present invention, showing non-vertical incident light L _yz at an angle θ _{yz in} the _yz plane. FIG. 1 is a schematic diagram of a light beam separation system according to an embodiment of the present invention. 1 is one of schematic cross-sectional views illustrating a first method of making a dielectric polarizing beam splitter according to an embodiment of the present invention. 1 is one of schematic cross-sectional views illustrating a first method of making a dielectric polarizing beam splitter according to an embodiment of the present invention. 1 is one of schematic cross-sectional views illustrating a first method of making a dielectric polarizing beam splitter according to an embodiment of the present invention. 1 is one of schematic cross-sectional views illustrating a first method of making a dielectric polarizing beam splitter according to an embodiment of the present invention. 1 is one of schematic cross-sectional views illustrating a first method of making a dielectric polarizing beam splitter according to an embodiment of the present invention. FIG. 5 is one of schematic cross-sectional views illustrating a second method of making a dielectric polarizing beam splitter, according to one embodiment of the present invention. FIG. 5 is one of schematic cross-sectional views illustrating a second method of making a dielectric polarizing beam splitter, according to one embodiment of the present invention. FIG. 5 is one of schematic cross-sectional views illustrating a second method of making a dielectric polarizing beam splitter, according to one embodiment of the present invention.

[Definition]
As used herein, the term “contrast” means the desired polarization transmission (eg, Tp) divided by the opposite polarization transmission (eg, Ts). Therefore, the contrast is equal to Tp / Ts.

  As used herein, the term “efficiency” means multiplying the transmittance (eg, Tp) of one polarization by the reflectance (eg, Rs) of the opposite polarization. Therefore, the efficiency is equal to Tp × Rs.

As used herein, the term “elongated” with respect to the high index region 13 _H and the low index region 13 _L is substantially longer than the width W _L of the low index region 13 _L (L >> W _L ), which is longer than the width W _{H of} the high refractive index region 13 _H (L >> W _H ), and means the length direction L. For example, in one aspect, the length direction L may be at least 10 times longer than the widths W _H and W _L , in another aspect, may be at least 100 times longer than the widths W _H and W _L , and in another aspect, The widths W _H and W _L may be at least 1000 times longer.

  As used herein, the term “polarizing beam splitter” or “PBS” is sufficient to transmit one polarization sufficiently for light incident from various angles, including an angle perpendicular to the plane of the substrate. Means a polarizer capable of sufficiently reflecting the opposite polarized light. For example, the PBS can, in one aspect, transmit at least 70% of one polarization, reflect at least 30% of the opposite polarization, and, in another aspect, transmit at least 80 of one polarization. May reflect at least 80% of the opposite polarization.

  As used herein, the term “thin film layer” means a continuous layer that cannot be divided into grids.

  Traditionally, metals (eg, aluminum) have been used as polarizing wires in the visible spectrum. Such a polarizer with a metal polarizing wire is relatively easy to produce, can achieve a relatively high contrast, and can achieve a high transmittance (eg, high Tp) of the desired polarization. Metals such as aluminum in such polarizers can absorb large amounts of light. For example, aluminum has a k value of about 4.8 to 8.4 across the visible spectrum. In some polarizer applications, this absorption is highly undesirable.

  FIGS. 1-5 show dielectric polarizing beam splitters (PBS) 10, 20a, 20b, 30, 40, which for the most part, substantially, or entirely are for light in the wavelength range used. It can be made of a substantially transparent dielectric material (eg, low k value / damping factor). Thereby, light loss due to absorption can be avoided. This can be a very important feature in some applications. PBSs 10, 20a, 20b, 30 and 40 can be made for use in the visible spectrum or other regions of electromagnetic radiation.

The PBSs 10, 20 a, 20 b, 30 and 40 include a lattice layer 13 that can be located on a substantially flat surface 11 _Pl of the substrate 11. The grating layer 13 may include an elongated, substantially parallel, alternating array of high index regions 13 _H and low index regions 13 _L. The lattice layer 13 may be located on a plane 13 _Pl substantially parallel to the plane 11 _Pl of the substrate 11.

The high refractive index region 13 _H may be made of a different dielectric material than the low refractive index region 13 _L, and there may be a clear boundary layer between these different materials. The high refractive index region 13 _H can be made of a solid dielectric material. The low refractive index region 13 _L may consist of a solid dielectric material, air, another gas, or a vacuum. The arrangement of the elongated, substantially parallel high refractive index region 13 _H and low refractive index region 13 _L may be a regular repeating arrangement.

In order to make the refractive index n _L of the low refractive index region 13 _L sufficiently lower than the refractive index n _H of the high refractive index region 13 _H , it is beneficial to improve the efficiency of the dielectric PBSs 10, 20a, 20b, 30 and 40 It can be. For example, the wavelength range of the assumed applications (e.g., visible light spectrum) over a refractive index n _H of the high refractive index region 13 _H, the difference between the refractive index n _L of the low refractive index region 13 _L, in one embodiment , Greater than 0.3 (n _H −n _L > 0.3), in another embodiment, greater than 1.0 (n _H −n _L > 1.0), and in another embodiment, greater than 1.3 (N _H −n _L > 1.3), in another embodiment, greater than 1.5 (n _H −n _L > 1.5), or in another embodiment, greater than 1.7 (n _H − n _L > 1.7). PBS 10, 20a, 20b, 30 and 40 can be selected by selecting a material of high refractive index region 13 _H having a high refractive index n _H (eg, greater than 2.0, 2.3 or 2.5 in the visible spectrum). The design can be improved.

In order to improve the efficiency of the dielectric PBS 10, 20a, 20b, 30 and 40, it may also be beneficial to meet one of the following two conditions (1 or 2). 1. The difference between the refractive index n _sub of the substrate 11 and the effective refractive index n _|| of the grating layer 13 for polarization parallel to the length direction L of the regions 13 _H and 13 _L is large, and the refractive index of the substrate 11 The difference between n _sub and the effective refractive index n _の of the grating layer 13 for polarization perpendicular to the length directions L of the regions 13 _H and 13 _L is small. For example, the lattice layer 13 and the substrate 11 can satisfy the following equation:
a. | N _sub -n _|| |> 0.3, | n _sub -n _|| |> 0.45, | n _sub -n _|| |> 0.6, | n _sub -n _|| 7, or | n _sub −n _|| |> 0.8, and b. _{| N sub - n ⊥ | <} 0.25, | n sub - n ⊥ | <0.2, | n sub - n ⊥ | <0.15, | n sub - n ⊥ | <0.1 or, | n _{sub -n⊥} | <0.05.
2. The difference between the refractive index n _sub of the substrate 11 and the effective refractive index n _率 of the grating layer 13 for polarization perpendicular to the longitudinal direction L of the regions 13 _H and 13 _L is large, and the refractive index n of the substrate 11 _{The difference} between _sub and the effective refractive index n _|| of the grating layer 13 for polarization parallel to the length direction L of the regions 13 _H and 13 _L is small. For example, the lattice layer 13 and the substrate 11 can satisfy the following equation:
a. _{| N sub - n ⊥ |>} 0.3, | n sub - n ⊥ |> 0.45, | n sub - n ⊥ |> 0.6, | n sub - n ⊥ |> 0.7 , or, | n _{sub -n⊥} |> 0.8, and b. | N _sub −n _|| | <0.25, | n _sub −n _|| | <0.2, | n _sub −n _|| | <0.15, | n _sub −n _|| 1, or | n _sub −n _|| | <0.05.
Equation 1 above. a. b. a, and 2. Duty cycle (W _H / P), n _sub , n _H , and n _L can be selected to achieve the desired relationship in b.

Ｗ_Ｌは、低屈折率領域１３_Ｌの幅である。Ｗ_Ｈは、高屈折率領域１３_Ｈの幅である。Ｐは、高屈折率領域１３_Ｈのピッチである。 The effective refractive index n _|| and n _の of the grating layer 13 can be approximated by the following equation for vertically incident light L _n (θ = 0, see FIGS. 4 and 5).

W _L is the width of the low refractive index region 13 _L. W _H is the width of the high refractive index region 13 _H. P is the pitch of the high refractive index region 13 _H.

For non-vertical incident light, the angle θ is the angle with respect to the z-axis, and the angle θ _xz is the angle with respect to the x-z plane (the plane that intersects the regions 13 _H and 13 _L and defines the plane of incidence). is there. For non-vertical incident light L _{xz at} an angle θ _xz (see FIG. 4), the effective refractive index n _|| (θ _xz ) of the grating layer 13 for polarization perpendicular to the plane of incidence depends on the incident angle θ _xz . Not affected. Therefore, n _|| (θ _xz ) = n _|| . However, the effective refractive index n _⊥ (θ _xz ) of the grating layer 13 for polarized light parallel to the plane of incidence depends on the incident angle θ _xz . An equation that approximates this effective refractive index n _⊥ (θ _xz ), which is the incident angle θ _xz , is as follows.

For non-vertical incident light L _yz (see FIG. 5) at angle θ _{yz in} the _yz plane (plane parallel to regions 13 _H and 13 _L and defining the plane of incidence) The effective refractive index n _|| (θ _yz ) of the grating layer 13 for polarized light and the effective refractive index n _⊥ (θ _yz ) of the grating layer 13 for polarized light perpendicular to the plane of incidence are incident angles θ. Not affected by. Therefore, n _|| (θ _yz ) = n _|| and n _⊥ (θ _yz ) = n _⊥ .

  PBS 10 (FIG. 1) is a simple dielectric PBS that includes only a single grating layer 13 on substrate 11 and no other layers. This PBS may have the advantages of low manufacturing costs and very low light absorption, but may have the disadvantage of low contrast. Adding a properly designed thin film layer 12 may improve efficiency (see PBS 20a, 20b, 30 and 40).

If the difference between the refractive index n _TF of the thin film layer 12 and the refractive index n _sub of the substrate 11 is small, the efficiency of the dielectric PBSs 20a, 20b, 30 and 40 can be improved. For example, the difference is lower than 0.6 (| n _TF −n _sub | <0.6) in one aspect and lower than 0.25 (| n _TF −n _sub | <0. 25), in another aspect, lower than 0.15 (| n _TF −n _sub | <0.15), and in another aspect, lower than 0.05 (| n _TF −n _sub | <0. 05).

In order to improve the efficiency of the dielectric PBS 20a, 20b, 30 and 40, it may also be beneficial to satisfy one of the following two conditions (3 or 4). 3. The difference between the refractive index n _TF of the thin film layer 12 and the effective refractive index n _|| of the grating layer 13 for polarization parallel to the length direction L of the regions 13 _H and 13 _L is large, and the thin film layer 12 The difference between the refractive index n _TF and the effective refractive index n _の of the grating layer 13 for polarized light perpendicular to the length directions L of the regions 13 _H and 13 _L is small. For example, the lattice layer 13 and the thin film layer 12 may satisfy the following equation.
a. | N _TF −n _|| |> 0.3, | n _TF −n _|| |> 0.45, | n _TF −n _|| |> 0.6, | n _TF −n _|| 7, or | n _TF −n _|| |> 0.8, and b. | N _{TF −n⊥} | <0.25, | n _{TF− n⊥} | <0.2, | n _{TF− n⊥} | <0.15, | n _{TF− n⊥} | <0.1, or | _{n TF - n ⊥ | <0.05} . 4). The difference between the refractive index n _TF of the thin film layer 12 and the effective refractive index n _の of the grating layer 13 for polarization perpendicular to the length direction L of the regions 13 _H and 13 _L is large, and the refraction of the thin film layer 12 The difference between the refractive index n _TF and the effective refractive index n _|| of the grating layer 13 for polarized light parallel to the length direction L of the regions 13 _H and 13 _L is small. For example, the lattice layer 13 and the thin film layer 12 may satisfy the following equation. a. | N _{TF −n⊥} |> 0.3, | n _{TF− n⊥} |> 0.45, | n _{TF− n⊥} |> 0.6, | n _{TF− n⊥} |> 0.7, or | n _{TF −n⊥} |> 0.8, and b. | N _TF −n _|| | <0.25, | n _TF −n _|| | <0.2, | n _TF −n _|| | <0.15, | n _TF −n _|| 1, or | n _TF −n _|| | <0.05.

Equation 3 above. a. b. a, and 4. Duty cycle (W _H / P), n _TF , n _H , and n _L can be selected to achieve the desired relationship in b.

The thin film layer 12 may have isotropic optical properties throughout the thin film layer. Thin layer 12, in the y-axis direction (region 13 _H and direction along the length L of 13 _L) and the x-axis direction (region 13 _H and 13 vertical to a longitudinal direction L of the _L), isotropic It can be. The thin film layer 12 can be composed of a single material (eg, a substantially homogeneous layer of silicon dioxide). Due to the fact that the material of the low refractive index region 13 _L is different from the material of the high refractive index region 13 _H , the lattice layer 13 is in the y-axis direction (the direction along the length direction L of the regions 13 _H and 13 _L ), etc. It may be anisotropic, but may be anisotropic in the x-axis direction (direction perpendicular to the length direction L of the regions 13 _H and 13 _L ).

As shown in FIG. 2 a, the lattice layer 13 can be adjacent to the substrate 11 and can be sandwiched between the thin film layer 12 and the substrate 11. As shown in FIG. 2 b, the thin film layer 12 can be adjacent to the substrate 11 and can be sandwiched between the lattice layer 13 and the substrate 11. In the lattice layer 13, the high refractive index region 13 _H may contact or adjacent to the low refractive index region 13 _L. The above relationship can be chosen to optimize the design of each dielectric PBS.

For some applications, the performance of the PBS may be improved by adding a grid layer 32 located between the lattice layer 13 and the thin film layer 12 (see FIG. 3). Grid layer 32 may comprise an array of elongated substantially parallel ribs 32 _r. Each rib 32 _r can be located between each high refractive index region 13 _H and the thin film layer 12 as shown, or is located between each low refractive index region 13 _L and the thin film layer 12. Obtain (not shown). The grid layer 32 can be made of the same material as the thin film layer 12. The grid layer 32 can be formed by using the high refractive index region 13 _H or the low refractive index region 13 _L as a mask for etching the thin film layer 12. In one embodiment, the grid layer 32 may have a thickness 32 _Th of 10-60 nanometers.

As shown in FIG. 4-5, both the lattice layer 13 and the thin film layer 12 may form a pair 43. The PBS 40 may further include at least one additional pair 43 in one aspect, and may include at least two additional pairs 43 in another aspect. The PBS 40 may, in another aspect, include at least one, fewer than fifteen pairs 43. The efficiency can be improved by the plurality of pairs 43. Defects in the relationship between the effective refractive indices n _⊥ and n _{|| of the} grating layer 13, the refractive index n _TF of the thin film layer 12, and the refractive index n _sub of the substrate 11 are compensated by additional pairs 43. Can be done. Since adding more pairs 43 can increase costs, it is preferable to optimize the relationship between the relevant indices of refraction as much as possible, and then add more pairs 43 as needed. Sometimes.

The material of the substrate 11, the lattice layer 13, the grid layer 32, and / or the thin film layer 12 can be a dielectric, and can be a non-polymerizable dielectric material. Examples of dielectric materials include Na ₃ AlF ₆ , MgF ₂ , ZnS, titanium oxide, SiO ₂ , Al ₂ O ₃ , and HfO ₂ . It may be beneficial for the material of the substrate 11, the grating layer 13, the grid layer 32 and / or the thin film layer 12 to have a low refractive index k value portion in the optical spectrum of the intended use. For example, the k value may be lower than 0.1 in one aspect, lower than 0.05 in another aspect, lower than 0.03 in another aspect, and lower than 0.01 in another aspect. . The k value may be lower than these values at one point in the spectrum of the intended application or in the entire spectrum of the intended application (eg, 400-700 nanometers).

In other aspects of PBS 10, 20a, 20b, 30 and 40, the design can be modified to optimize performance for each particular design. For example, as shown in Figure 1, the thickness _{13 LTh} of the low refractive index region 13 _L may be the same as the thickness _{13 HTH} the high refractive index region 13 _H (thus, the grating layer 13, a single thickness 13 _Th ). As shown in Figure 1, the upper surface of the low refractive index region 13 _L, and the upper surface of the high refractive index region 13 _H may be terminated in a common plane 13 _PT. As shown in Figure 1, the bottom surface of the low refractive index region 13 _L, and the bottom surface of the high refractive index region 13 _H may be terminated in a common plane 13 _PB. As shown in Figure 3, the thickness _{13 LTh} of the low refractive index region 13 _L may be larger than the thickness _{13 HTH} high refractive index region 13 _H. Although not shown, the thickness _{13 LTh} of the low refractive index region 13 _L may be be less than the thickness _{13 HTH} high refractive index region 13 _H.

  If it is desirable to minimize high-order diffraction, it may be beneficial to have a pitch P that is less than or less than half the lowest wavelength in the wavelength spectrum used. For example, when used in visible light, the pitch P is less than 400 nanometers in one aspect, or less than 200 nanometers in another aspect.

In order to suppress the high-order diffraction to a minimum, the low refractive index region 13 _L width W _{L of,} and / or, the width W _H of the high refractive index region 13 _H, either less than the minimum wavelength of the wavelength spectrum to be used, or , Making it smaller than half of it can be beneficial (see FIGS. 4-5). For example, the use of visible light, the width _{W L} of the low refractive index region 13 _L, and / or the width _{W H} of the high refractive index region 13 _H, in one embodiment, less than 400 nanometers, another aspect In another embodiment, it may be less than 200 nanometers, in another embodiment, less than 100 nanometers, and in another embodiment, less than 60 nanometers.

The lattice layer 13 and the thin film layer 12 may be optical thin films. For example, the grating layer 13 has a thickness of 13 _Th , and the thin film layer 12 is in one aspect less than one wavelength or in another aspect for light in the assumed wavelength range of use of PBS. It may have a thickness of 12 _Th less than two wavelengths. The lattice layer 13 has a thickness of 13 _Th , and the thin film layer 12 can in another embodiment have a thickness of 12 _Th less than 400 nanometers.

  The dielectric PBSs 10, 20a, 20b, 30 and 40 described herein can be located in a glass cube, so the back focal length is short, durable and easy to assemble into an optical system. While it may have the advantage of a prism, it can also be polarized in a much larger range of light incident angles than a MacNeille prism. The dielectric PBSs 10, 20a, 20b, 30, 40 described herein may improve efficiency compared to other wire grid polarizing beam splitter designs.

[Light separation system and method of use]
FIG. 6 shows a light separation system 60. The light source 61 can be arranged to irradiate light 62 (eg, visible light) to a PBS 65 that can be made according to one of the embodiments described herein. The PBS 65 may separate the light 62 into a transmitted beam 64 (which may include primarily one polarization, eg, p-polarization) and a reflected beam 63 (which may include primarily opposite polarization, eg, s-polarization). Desirably, the incident light 62 is equal to the sum of the transmitted beam 64 and the reflected beam 63 (light 62 = transmitted beam 64 + reflected beam 63). However, due to absorption, incident light 62 can be larger than the sum of transmitted beam 64 and reflected beam 63 (light 62> transmitted beam 64 + reflected beam 63). Therefore, a larger, more powerful, and more expensive light source 61 may be required, increasing the need for cooling, resulting in increased cost, weight, size, and noise of the system 60. Is not desirable. Therefore, it can be beneficial to minimize absorption and to approach the ideal state where incident light 62 is equal to the sum of transmitted beam 64 and reflected beam 63.

  By making all or substantially all of the PBS 65 from a dielectric material, absorption can be minimized. Thus, for example, in one aspect, at least 90% of incident light 62 on PBS can be reflected or transmitted by PBS 65 (0.9 × light 62 ≦ reflected beam 63 + transmitted beam 64), and in another aspect, PBS At least 95% of the incident light 62 above may be reflected or transmitted by the PBS 65, and in another embodiment, at least 98% of the incident light 62 on the PBS may be reflected or transmitted by the PBS 65, in another embodiment. , At least 99% of the incident light 62 on the PBS may be reflected or transmitted by the PBS 65.

The methods described herein using one of PBS 10, 20a, 20b, 30 or 40 may include the following steps.
1. PBS 10, 20a, 20b, 30 or 40 is arranged in the light source 61.
2. In one aspect, at least 90% of incident light 62 is transmitted or reflected, in another aspect, at least 95 of incident light is transmitted or reflected, and in another aspect, at least 98 of incident light is transmitted or reflected, and In this embodiment, at least 99% of the incident light is transmitted or reflected.

[Example design]
The following is an exemplary design of a plate-like dielectric PBS designed for 550 nanometer wavelength light L _xz incident from air at an angle θ _xz = 45 °. 1. The high refractive index region 13 _H is TiO ₂ and n _H ≈2.58, and the low refractive index region 13 _L is air and n _L ≈1.0. n _H - n _L = 1.58.
2. The thin film layer 12 is MgF ₂ and n _TF ≈1.38.
3. The substrate 11 is a Borofloat glass plate, and n _sub = 1.50.
4). The pitch is 144 nanometers.
5. The duty cycle (W _H / P) is 65%.
6). Vertical incident light _{L n: n || = 2.17,} n ⊥ = 1.50.
7). Non-vertical incident light L _xz at an angle of 45 ° along the x-z plane: n _|| (45 °) = 2.17, n _⊥ (45 °) = 1.58.
8). | N _TF −n _∥ | = 0.20, | n _sub −n _∥ | = 0.
9. | _NTF −n _||| = 0.79, | _nsub −n _||| = 0.67.
10. | N _TF −n _sub | = 0.12.

The following is an exemplary design of a dielectric PBS cube designed for broadband visible light L _yz incident on glass at an angle θ _yz = 45 °.
1. The high refractive index region 13 _H is TiO ₂ and n _H ≈2.58, and the low refractive index region 13 _L is spin-on-glass and n _L ≈1.17. n _H - n _L = 1.41.
2. The thin film layer 12 is HfO ₂ and n _TF ≈1.93.
3. The substrate 11 is glass, and n _sub ≈1.88. The medium of incident light is also glass, and n _sub ≈1.88.
4). The pitch is 120 nanometers.
5. The duty cycle (W _H / P) is 40%.
6). Vertical incident light _{L n: n || = 1.87,} n ⊥ = 1.42.
7). Non-vertical incident light L _yz at an angle of 45 ° along the x-z plane: n _|| (45 °) = 1.87, n _⊥ (45 °) = 1.42.
8). | N _{TF −n⊥} | = 0.51, | n _{sub− nｎ} | = 0.46.
9. | N _TF −n _|| | = 0.06, | n _TF −n _|| | = 0.01.
10. | N _TF −n _sub | = 0.05.

[Overview of design]
To summarize the design considerations described above, the range of light incident angles is wide, the transmittance of one polarization is high (eg, high Tp), and the reflection of the opposite polarization is high (eg, Rs is controlled). High, or Rs is controlled to the desired value), high efficiency, short back focal length of optical system, low light absorption, and / or easy assembly into optical system Advantageous PBSs can be made with the following design considerations.

  First, the beam splitter is made, for the most part, substantially or entirely from a dielectric material that is substantially transparent to light in the wavelength range used (eg, a low k value). obtain.

Second, the beam splitter may include at least one grating layer 13. The grating layer 13 may comprise an elongated, substantially parallel, alternating array of high index regions 13 _H and low index regions 13 _L. When the difference between the refractive indices of these two regions 13 _H and 13 _L is large (ie, the value of n _H −n _L is large), the performance can be improved.

Third, if the thin film layer 12 is used, _{| n TF} - _{n ⊥ |} is _{large, | n} TF - _{n || |} so decreases, or, _{| n TF} - _{n ⊥ |} is small, | Design so that n _TF −n _||| If the thin film layer 12 is not _{used, | n sub} - _{n ⊥ |} is _{large, | n} sub - _{n || |} so decreases, _{or, | n sub} - _{n ⊥ |} is _{small, | n} sub - _{n | | |} designed to increase. If the difference between n _TF / n _sub and n _⊥ or n _|| is small, it is possible to minimize reflection when one polarization passes through the layer boundary. Theoretically, if n _TF / n _sub = n _⊥ or n _TF = n _|| / n _sub , this polarization will not be reflected at the boundary between the thin film layer 12 and the grating layer 13. If the difference between n _TF / n _sub and n _⊥ or n _|| is large, the reflection of the other polarization can be large. In theory, it is beneficial to make this difference as large as possible.

Fourth, it is designed so that | n _TF −n _sub | This makes it possible to minimize the reflection of this polarization at any boundary between the substrate and the thin film layer 12 or the grating layer 13. Theoretically, the case of n _TF = n _sub is optimal.

  In a practical design, tradeoffs may exist because the material properties are not ideal. One design can be optimized primarily for the transmission of one polarization, but at the expense of another desired property. Another design can be optimized primarily for reflection of one polarization, but at the expense of another desired property.

  Due to defects in available materials and manufacturing defects, actual designs usually do not meet ideal conditions. Thus, as shown in the exemplary design above, the terms “large” and “small” are relative. Such defects can be compensated at least in part by increasing the number of pairs 43. However, increasing the number of pairs 43 can increase manufacturing costs, so there may be a trade-off between improving performance and avoiding increased polarizer costs.

[How to make]
The first method of making a dielectric PBS can include some or all of the following steps (steps 1 and 2 can be performed in any order, and step 3 follows steps 1 and 2 Can be implemented).
1. The lattice layers 13 are formed by sequentially performing the following steps a to c.
a. An array of parallel first regions 13 _R1 is formed on the substrate 11. For example, the material 13 _M1 is sputtered on the substrate 11 (see FIG. 7), and then the material 13 _M1 is patterned and etched to form the first region 13 _R1 (see FIG. 8). If it is desired to create the grid layer 32, the first region _13R1 can be used as a mask to etch into the underlying material (eg, the thin film layer 12 or the substrate 11).
b. The elongated grooves 83 between the first regions 13 _R1 and the first regions 13 _R1 are filled with the second material 13 _M2 (for example, spin-on or ALD). See Figure 8-9.
c. As the top _{13 R1T} the first region _{13 R1} does not include the second material _{13 M2} substantially, by etching the second material _{13 M2,} to form the second region _{13 R2} in the groove 83. See Figures 9-10.
2. A thin film layer 12 is formed (eg, by sputtering) on the surface of the substrate 11. See FIG.
3. Repeat steps 1-2 (this step 3 is repeated multiple times).
Either the first region 13 _R1 or the second region 13 _R2 can be the high refractive index region 13 _H , and the other of the first region 13 _R1 or the second region 13 _R2 is the low refractive index region 13 _L. obtain.

A second method of making a dielectric PBS may include some or all of the following steps (steps 1 and 2 can be performed in any order, and step 3 follows steps 1 and 2 Can be implemented).
1. A thin film layer 12 is formed (eg, by sputtering) on the surface of the substrate 11. See FIG.
2. The lattice layer 13 is formed by forming an array of parallel and elongated high refractive index regions 13 _H on the surface of the substrate 11. For example, the material of the high refractive index region 13 _H is sputtered on the substrate 11, and then patterning and etching are performed to form the high refractive index region 13 _H. As shown in FIG. 3, if it is desired to create the grid layer 32, the high refractive index region 13 _H can be used as a mask to etch the thin film layer 12. The groove filled with air between the high refractive index regions 13 _H may be the low refractive index region 13 _L. See FIG.
3. Repeat steps 1-2 (step 3 can be repeated multiple times). See FIG. It may be difficult to deposit the thin film layer 12 on the grating layer 13 without filling the low refractive index region 13 _L with the material of the thin film layer. To minimize the filling of the low index region 13 _L with the material of the thin film layer 12, deposition at a large oblique angle (eg, 80 °), or US Patent Application No. 2012, incorporated herein by reference. / 0075699 may be used.

Claims (20)

A dielectric polarization beam splitter (PBS),
a. Comprising a substrate having a substantially planar surface;
b. Comprising a lattice layer and a thin film layer disposed on the plane of the substrate;
c. The lattice layer includes an array of a plurality of alternating high refractive index regions and a plurality of low refractive index regions that are elongated and substantially parallel.
d. The lattice layer is disposed in a plane substantially parallel to the plane of the substrate;
e. The refractive index (n _L ) of the plurality of low refractive index regions is lower than the refractive index (n _H ) of the plurality of high refractive index regions,
f. The lattice layer and the thin film layer are:
i. | N _TF −n _|| |> 0.7 and | n _{TF −n⊥} | <0.25, or
ii. | N _{TF −n⊥} |> 0.7 and | n _TF −n _|| | <0.25,
Satisfy the equation
iii. here,
1. n _TF is the refractive index of the thin film layer,
2. n _|| is the effective refractive index of the grating layer for polarized light parallel to the length direction of the plurality of high refractive index regions and the plurality of low refractive index regions;
3. n _⊥ is the effective refractive index of the grating layer for polarized light perpendicular to the length direction of the plurality of high refractive index regions and the plurality of low refractive index regions,
4). n _TF is the refractive index of the thin film layer,
g. The material of the lattice layer is a dielectric, and the material of the thin film layer is a dielectric.
Dielectric polarization beam splitter (PBS). A dielectric polarization beam splitter (PBS),
a. Comprising a substrate having a substantially planar surface;
b. Comprising a lattice layer and a thin film layer disposed on the plane of the substrate;
c. The lattice layer includes an array of a plurality of alternating high refractive index regions and a plurality of low refractive index regions that are elongated and substantially parallel.
d. The lattice layer is disposed in a plane substantially parallel to the plane of the substrate;
e. The refractive index (n _L ) of the plurality of low refractive index regions is lower than the refractive index (n _H ) of the plurality of high refractive index regions,
f. The lattice layer and the thin film layer are:
i. | N _TF −n _|| |> 0.45 and | n _{TF −n⊥} | <0.1, or
ii. | N _{TF −n⊥} |> 0.45 and | n _TF −n _|| | <0.1,
Satisfy the equation
iii. here,
1. n _TF is the refractive index of the thin film layer,
2. n _|| is the effective refractive index of the grating layer for polarized light parallel to the length direction of the plurality of high refractive index regions and the plurality of low refractive index regions;
3. n _⊥ is the effective refractive index of the grating layer for polarized light perpendicular to the length direction of the plurality of high refractive index regions and the plurality of low refractive index regions,
4). n _TF is the refractive index of the thin film layer,
g. The plurality of materials of the lattice layer and the thin film layer are dielectric materials in which the k value portion of the refractive index is smaller than 0.05.
Dielectric polarization beam splitter (PBS). 3. The refractive index (n _L ) of the plurality of low refractive index regions and the refractive index (n _H ) of the plurality of high refractive index regions satisfy an equation of n _H −n _L > 1.3. PBS described in 1. A dielectric polarization beam splitter (PBS),
a. Comprising a substrate having a substantially planar surface;
b. Comprising a lattice layer and a thin film layer disposed on the plane of the substrate;
c. The lattice layer includes an array of a plurality of alternating high refractive index regions and a plurality of low refractive index regions that are elongated and substantially parallel.
d. The lattice layer is disposed in a plane substantially parallel to the plane of the substrate;
e. The refractive index (n _L ) of the plurality of low refractive index regions is lower than the refractive index (n _H ) of the plurality of high refractive index regions,
f. The material of the lattice layer is a dielectric, and the material of the thin film layer is a dielectric.
Dielectric polarization beam splitter (PBS). 5. The refractive index (n _L ) of the plurality of low refractive index regions and the refractive index (n _H ) of the plurality of high refractive index regions satisfy an equation of n _H −n _L > 1.5. PBS.
5. The refractive index (n _L ) of the plurality of low refractive index regions and the refractive index (n _H ) of the plurality of high refractive index regions satisfy an equation of n _H −n _L > 1.3. PBS. The lattice layer and the thin film layer are:
a. | N _TF −n _|| |> 0.7 and | n _{TF −n⊥} | <0.25, or
b. | N _{TF −n⊥} |> 0.7 and | n _TF −n _|| | <0.25
Satisfy the equation
c. here,
i. For vertically incident light

ii. For vertically incident light

iii. n _TF is the refractive index of the thin film layer,
iv. W _L is the width of the plurality of low refractive index regions,
v. W _H is the width of the plurality of high refractive index regions,
vi. P is the pitch of the plurality of high refractive index regions,
The PBS according to claim 4. The lattice layer and the thin film layer are:
a. | N _TF −n _|| |> 0.45 and | n _{TF −n⊥} | <0.1, or
b. | N _{TF −n⊥} |> 0.45 and | n _TF −n _|| | <0.1
Satisfy the equation
c. here,
i. For vertically incident light

ii. For vertically incident light

iii. n _TF is the refractive index of the thin film layer,
iv. W _L is the width of the plurality of low refractive index regions,
v. W _H is the width of the plurality of high refractive index regions,
vi. P is the pitch of the plurality of high refractive index regions,
The PBS according to claim 4. The lattice layer and the thin film layer are:
a. | N _TF −n _|| |> 0.7 and | n _{TF −n⊥} | <0.25, or
b. | N _{TF −n⊥} |> 0.7 and | n _TF −n _|| | <0.25
Satisfy the equation
c. here,
i. n _TF is the refractive index of the thin film layer,
ii. n _|| is the effective refractive index of the grating layer for polarized light parallel to the length direction of the plurality of high refractive index regions and the plurality of low refractive index regions;
iii. n _⊥ is the effective refractive index of the grating layer for polarized light perpendicular to the length direction of the plurality of high refractive index regions and the plurality of low refractive index regions,
iv. n _TF is the refractive index of the thin film layer,
The PBS according to claim 4. The lattice layer and the thin film layer are
a. | N _TF −n _|| |> 0.45 and | n _{TF −n⊥} | <0.1, or
b. | N _{TF −n⊥} |> 0.45 and | n _TF −n _|| | <0.1,
Satisfy the equation
c. here,
i. n _TF is the refractive index of the thin film layer,
ii. n _|| is the effective refractive index of the grating layer for polarized light parallel to the length direction of the plurality of high refractive index regions and the plurality of low refractive index regions,
iii. n _⊥ is the effective refractive index of the grating layer for polarized light perpendicular to the length direction of the plurality of high refractive index regions and the plurality of low refractive index regions,
iv. n _TF is the refractive index of the thin film layer,
The PBS according to claim 4. The thin film layer and the substrate satisfy the equation | n _TF −n _sub | <0.15;
a. n _TF is the refractive index of the thin film layer,
b. n _sub is the refractive index of the substrate,
The PBS according to claim 4. The plurality of materials of the substrate, the lattice layer, and the thin film layer are dielectric materials in which the k value portion of the refractive index is smaller than 0.03.
The PBS according to claim 4.   The PBS of claim 4, wherein the plurality of materials of the substrate, the lattice layer, and the thin film layer are non-polymerizable dielectric materials. a. The lattice layer and the thin film layer together constitute a pair,
b. The PBS of claim 4, wherein the PBS further comprises at least two additional pairs. a. The lattice layer and the thin film layer constitute a pair,
b. The PBS comprises at least one, fewer than 15 pairs;
The PBS according to claim 4.   The PBS of claim 4, wherein the lattice layer is in contact with the thin film layer. A polarizing beam splitter (PBS) for the visible spectrum,
a. A lattice layer is disposed on a substantial plane of the substrate;
b. The lattice layer includes an array of a plurality of alternating high refractive index regions and a plurality of low refractive index regions that are elongated and substantially parallel.
c. The lattice layer is disposed in a plane substantially parallel to the plane of the substrate;
d. The refractive index (n _L ) of the plurality of low refractive index regions and the refractive index (n _H ) of the plurality of high refractive index regions are in the range of 400 to 700 nanometers, and n _H −n _L > 1.3. Satisfy the equation,
e. The material of the lattice layer is a dielectric,
Polarizing beam splitter (PBS) for the visible spectrum. a. Place the PBS in a visible light source,
b. Transmit or reflect at least 95% of incident visible light;
The method of using the PBS according to claim 17. a. The upper surfaces of the plurality of low refractive index regions and the upper surfaces of the plurality of high refractive index regions are terminated at a common surface,
b. The bottom surfaces of the plurality of low refractive index regions and the bottom surfaces of the plurality of high refractive index regions are terminated at a common plane.
The PBS of claim 17.   The PBS of claim 17, wherein the plurality of materials of the lattice layer have a plurality of k values less than 0.01 in the range of 400-700 nanometers.

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